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  <div class="section" id="numpy-partition">
<h1>numpy.partition<a class="headerlink" href="#numpy-partition" title="Permalink to this headline">¶</a></h1>
<dl class="function">
<dt id="numpy.partition">
<code class="sig-prename descclassname">numpy.</code><code class="sig-name descname">partition</code><span class="sig-paren">(</span><em class="sig-param">a</em>, <em class="sig-param">kth</em>, <em class="sig-param">axis=-1</em>, <em class="sig-param">kind='introselect'</em>, <em class="sig-param">order=None</em><span class="sig-paren">)</span><a class="reference external" href="https://github.com/numpy/numpy/blob/v1.18.1/numpy/core/fromnumeric.py#L658-L747"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#numpy.partition" title="Permalink to this definition">¶</a></dt>
<dd><p>Return a partitioned copy of an array.</p>
<p>Creates a copy of the array with its elements rearranged in such a
way that the value of the element in k-th position is in the
position it would be in a sorted array. All elements smaller than
the k-th element are moved before this element and all equal or
greater are moved behind it. The ordering of the elements in the two
partitions is undefined.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 1.8.0.</span></p>
</div>
<dl class="field-list simple">
<dt class="field-odd">Parameters</dt>
<dd class="field-odd"><dl class="simple">
<dt><strong>a</strong><span class="classifier">array_like</span></dt><dd><p>Array to be sorted.</p>
</dd>
<dt><strong>kth</strong><span class="classifier">int or sequence of ints</span></dt><dd><p>Element index to partition by. The k-th value of the element
will be in its final sorted position and all smaller elements
will be moved before it and all equal or greater elements behind
it. The order of all elements in the partitions is undefined. If
provided with a sequence of k-th it will partition all elements
indexed by k-th  of them into their sorted position at once.</p>
</dd>
<dt><strong>axis</strong><span class="classifier">int or None, optional</span></dt><dd><p>Axis along which to sort. If None, the array is flattened before
sorting. The default is -1, which sorts along the last axis.</p>
</dd>
<dt><strong>kind</strong><span class="classifier">{‘introselect’}, optional</span></dt><dd><p>Selection algorithm. Default is ‘introselect’.</p>
</dd>
<dt><strong>order</strong><span class="classifier">str or list of str, optional</span></dt><dd><p>When <em class="xref py py-obj">a</em> is an array with fields defined, this argument
specifies which fields to compare first, second, etc.  A single
field can be specified as a string.  Not all fields need be
specified, but unspecified fields will still be used, in the
order in which they come up in the dtype, to break ties.</p>
</dd>
</dl>
</dd>
<dt class="field-even">Returns</dt>
<dd class="field-even"><dl class="simple">
<dt><strong>partitioned_array</strong><span class="classifier">ndarray</span></dt><dd><p>Array of the same type and shape as <em class="xref py py-obj">a</em>.</p>
</dd>
</dl>
</dd>
</dl>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
<dl class="simple">
<dt><a class="reference internal" href="numpy.ndarray.partition.html#numpy.ndarray.partition" title="numpy.ndarray.partition"><code class="xref py py-obj docutils literal notranslate"><span class="pre">ndarray.partition</span></code></a></dt><dd><p>Method to sort an array in-place.</p>
</dd>
<dt><a class="reference internal" href="numpy.argpartition.html#numpy.argpartition" title="numpy.argpartition"><code class="xref py py-obj docutils literal notranslate"><span class="pre">argpartition</span></code></a></dt><dd><p>Indirect partition.</p>
</dd>
<dt><a class="reference internal" href="numpy.sort.html#numpy.sort" title="numpy.sort"><code class="xref py py-obj docutils literal notranslate"><span class="pre">sort</span></code></a></dt><dd><p>Full sorting</p>
</dd>
</dl>
</div>
<p class="rubric">Notes</p>
<p>The various selection algorithms are characterized by their average
speed, worst case performance, work space size, and whether they are
stable. A stable sort keeps items with the same key in the same
relative order. The available algorithms have the following
properties:</p>
<table class="docutils align-default">
<colgroup>
<col style="width: 30%" />
<col style="width: 13%" />
<col style="width: 23%" />
<col style="width: 21%" />
<col style="width: 13%" />
</colgroup>
<thead>
<tr class="row-odd"><th class="head"><p>kind</p></th>
<th class="head"><p>speed</p></th>
<th class="head"><p>worst case</p></th>
<th class="head"><p>work space</p></th>
<th class="head"><p>stable</p></th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><p>‘introselect’</p></td>
<td><p>1</p></td>
<td><p>O(n)</p></td>
<td><p>0</p></td>
<td><p>no</p></td>
</tr>
</tbody>
</table>
<p>All the partition algorithms make temporary copies of the data when
partitioning along any but the last axis.  Consequently,
partitioning along the last axis is faster and uses less space than
partitioning along any other axis.</p>
<p>The sort order for complex numbers is lexicographic. If both the
real and imaginary parts are non-nan then the order is determined by
the real parts except when they are equal, in which case the order
is determined by the imaginary parts.</p>
<p class="rubric">Examples</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">a</span> <span class="o">=</span> <span class="n">np</span><span class="o">.</span><span class="n">array</span><span class="p">([</span><span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">1</span><span class="p">])</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">np</span><span class="o">.</span><span class="n">partition</span><span class="p">(</span><span class="n">a</span><span class="p">,</span> <span class="mi">3</span><span class="p">)</span>
<span class="go">array([2, 1, 3, 4])</span>
</pre></div>
</div>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">np</span><span class="o">.</span><span class="n">partition</span><span class="p">(</span><span class="n">a</span><span class="p">,</span> <span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">3</span><span class="p">))</span>
<span class="go">array([1, 2, 3, 4])</span>
</pre></div>
</div>
</dd></dl>

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